The present invention concerns a charging member for charging a material to be charged such as a light sensitive material for use in electrophotography and electrostatic recording processes in image forming apparatus such as electrophotographic copying machines and printers. More specifically, it relates to a charging member to be pressed on the surface of a material to be charged such as a light sensitive material and a dielectric material for uniformly charging the surface of the material to be charged, and a charging device.
In electrophotographic apparatus, uniform charge is applied to the surface of a material to be charged such as a light sensitive material or a dielectric material. A method of conducting the charging function by using corona generation by applying a high voltage to metal wires has been adopted as a charging treatment means. However, the corona charging method involves a drawback that corona-induced products such as ozone and nitrogen oxides (NOx) formed upon charging and denature the surface of the light sensitive material to deteriorate the light sensitive material or cause image blurring, and that the contamination of the wires gives an undesired effect on the image quality, leading to image deletions.
In addition to the non-contact method described above, there is a contact method of conducting charging by bringing a charging member into contact, or near contact, with a material to be charged. The contact, or near contact, type charging method has an advantage that a voltage to be applied to the charging member is generally low and the amount of ozone formed is extremely small. However, it has three major drawbacks. The first is the electrical stability of the selected material set over the life of the said contact-charging device. Depending on the type of conduction method selected, the conduction medium can drift within the material causing the electrical properties of the charging member to change over time, thereby causing non-uniform charging or stressing of the high voltage power supply that applies high voltage to the charging member. The second difficulty is the achievement of uniform charge in the length-wise direction of the charging member. The uniformity of the charge applied by the charging member is largely attributed to the dimensional uniformity of the contact interface between the said charging member and the member to be charged. The last major challenge in contact type charging is to overcome non-uniform charging caused by toner and toner additive contamination that occurs on the surface of the charging member.